Do Now: 5/2 1. What frequency is radiation with a wavelength of 8.2 x cm? 2. How far would light travel in 8.5 minutes?

Do Now: 5/2 What frequency is radiation with a wavelength of 8.2 x cm?

Do Now (5/2/12): Take out your art piece. Share with a neighbor. Of the two styles of art that we have used so far (realism and mixed media), which did you like better? Why?

Light Behavior B-Course 5/2/12

The Ray Model of Light Light is a ray Its direction is only changed by another object

Reflection Light waves bouncing off of an obstacle

Refraction Occurs when waves pass from one medium to another. When a wave crosses a boundary, the direction it is moving undergoes a change; the path is "bent."

Refraction

Refraction

Diffraction The bending of light around a barrier or opening

Dispersion Isaac Newton showed that light shining through a prism will be separated into its different wavelengths and will show the various colors that make up visible light Dispersion: the separation of visible light into its different colors

Dispersion

Dispersion

White Light When all wavelengths of the visible light spectrum strike your eye at the same time, white is perceived.

The Law of Reflection When light is reflected off a surface, the angle of incidence ( Θ i ) is always equal to the angle of reflection ( Θ r ).

Normal The normal: the line perpendicular to the surface Angles are always measured relative to the normal normal

Index of Refraction Unique to every material Represented by n Always greater than 1

Calculating n The speed of light is constant in a vacuum (c=3x10 8 m/s) v=speed of light in another material n=index of refraction

Practice: Use the rest of class to work on the paper “Refraction and Light Waves.” It is due Tuesday!

Do Now (5/3/12): 1. What does the term “dispersion” describe? 2. The index of refraction “n” is always greater than what number? 3. The speed of light is constant in what?

Drawing Ray Diagrams 5/3/12

Step 1: Draw the boundary, label n’s: n=1.05 n=1.13

Step 2: Draw the normal: n=1.05 n=1.13

Step 3: Draw the incident ray: n=1.05 n=1.13

Step 4: Draw the refracted ray: n=1.05 n=1.13

Drawing Refraction Include boundary, incident ray, refracted ray, normal, and angles

Do Now: 1. Draw a diagram for the following scenario: Light traveling in water strikes glass at an angle of 40˚. It refracts at an angle of 32˚. 2. What is the speed of light in glass if the index of refraction is 1.52?

Snell’s Law of Refraction

Example: A light beam in air hits a sheet of crown glass at an angle of 30˚. At what angle is the light refracted?

Practice: Use the rest of class to draw diagrams of refraction, then continue working on your homework. It is due Tuesday!

Do Now (5/4/12): pds 1 & 2 Please pass in your Do Now’s, then sit and wait quietly for instructions

Do Now (5/4/12): A light beam in air hits a sheet of crown glass at an angle of 30˚. 1. Draw a ray diagram. 2. At what angle is the light refracted?

Practice: Use the rest of class to work on either your homework or your art piece. Hw is due Tuesday, and your art piece is due Wednesday!!!

Angle of Refraction if then

Frequency When a beam of light enters one medium from another, the frequency stays constant

Total Internal Reflection Occurs when light traveling from a region of higher index of refraction to a lower one strikes the boundary at an angle such that all light reflects back

Critical Angle Specific angle of incidence when the refracted ray lies along the boundary of the two media ( Θ r =90˚)

Total Internal Reflection Occurs when

Critical Angle n r MUST be less than n i !!!!

Example: What is the critical angle if light travels from water to air?

Do Now: Carbon disulfide (n=1.63) is poured into a container made of crown glass (n=1.52). What is the critical angle for total reflection of a ray in the liquid when it is incident on the liquid-to-glass surface?

Practice: Please use the rest of class to finish the paper “Critical Angle Classwork” It is due by the end of class! When you finish begin working on your next art piece

Sources of light Luminous – an object that emits light Illuminated – an object that becomes visible as a result of light reflecting off it

Illuminated Opaque – do not transmit, only reflect light Transparent – transmit light Translucent – transmit light but do not allow objects to be clearly seen through them

Luminous Flux (P): The rate at which light energy is emitted from a luminous source Unit: lumens (lm) 100 W ~ 1750 lm *a measure of the number of rays emitted

Illuminance (E) The rate at which lights strikes a surface Unit: lux (lx)

Point Source Illuminance: r=distance from object to point source of light

Example: What is the illuminance on your desktop if it is lit by a 1750 lm lamp that is 2.5 m above your desk?

Luminous Intensity Luminous flux per solid angle Unit: candela (cd)

Example: In a library, an overhead lamp is 1.80 m above a reading table, and it produces 150 lux of illumination on the reading table. A) Find the luminous intensity of this lamp in candelas. B) Find the luminous flux, in lumens, emitted by the lamp. C) How high above the table should a 990 cd (12440 lm) lamp be suspended to produce the same illuminance on the table?

Do Now: After passing from one material into another, a light ray makes an angle of refraction of 11.63º. If it came from a medium with index of refraction 1.74 and passed into a medium with index of refraction 1.35, what angle of incidence did the ray make when it was in the first medium?

Do Now: In a library, an overhead lamp is 3.4 m above a reading table, and it produces 750 lux of illumination on the reading table. A) Find the luminous flux, in lumens, emitted by the lamp. B) Find the luminous intensity of this lamp in candelas. C) How high above the table should a 990 cd (12440 lm) lamp be suspended to produce the same illuminance on the table?